HART Hart is an acronym for Highway addressable remote transducers.HART is a bidirectional master-slave field communications protocol developed in the late 1980's to facilitate communication between intelligent field instruments and host systems by Rosemount Inc. Later it was developed into an open protocolIt makes use of the Bell 202 Frequency Shift Keying (FSK) standard to superimpose digital communication signals at a low level on top of the 4-20mA.It communicates without interrupting the 4-20mA signal and allows a host application (master) to get two or more digital updates per second from a field device HART PROCESS TRANSMITTER:-.

HART COMMUNICATIONS The transmitting device begins by turning ON its carrier and loading the first byte to be transmitted into its UART. The UART converts each transmitted byte into a 11 bit serial character.

PROTOCOL Only one HART device can talk at a time. A Master typically sends a command and then expects a reply. A Slave waits for a command and then sends a reply. A Slave accesses the network as quickly as possible in response to a Master. The command and associated reply are called a transaction. There are typically periods of silence (nobody talking) between transactions. Network access by Masters requires arbitration which is based on monitoring of network traffic and implementation of timers. If two Masters are present and both are synchronized, then they will use the network alternately . A Slave (normally) has a unique address to distinguish it from other Slaves. Addresses are either 4 bits or 38 bits. The long address consists of the lower (least significant) 38 bits of a 40-bit unique identifier. Each command or reply is a message, varying in length from 10 or 12 bytes to typically 20 or 30 bytes Hart Communications contd. The preamble is allowed to vary in length, depending on the Slave's requirements. The status field (2 bytes) occurs only in replies by HART Slave devices. If a Slave does not execute a command, the status shows this and usually indicates why. Several possible reasons are: 1. The Slave received the message in error. (This can also result in no reply.) 2. The Slave doesn't implement this command. 3. The Slave is busy. 4. The Slave was told to do something outside of its capability(range number too large or small, for example). 5. The Slave is write-protected and was told to change a protected parameter. Commands are one of 3 types: Universal, Common Practice, and Device Specific (Proprietary). SLAVE REPLY ALGORITHM

COMMANDS FROM HOST TO DEVICE Set Primary Variable Units Set Upper Range Set Lower Range Set Damping Value Set Message Set Tag Set Date Set Descriptor Perform Loop Test - Force loop current to specific value Initiate Self Test - Start device self test Get More Status Available Information Codes vary by manufacturer/device HART DATA OVERVIEW CONTD DEVICE IDENTIFICATION:- Instrument Tag - User defined, up to 8 characters Descriptor - User defined, up to 16 characters Manufacturer Name (Code) - Code established by HCF and set by manufacturer Device Type and Revision - Set by manufacturer Device Serial Number - Set by manufacturer Sensor Serial Number - Set by manufacturer

CALIBRATION INFORMATION FOR 4-20MA TRANSMISSION OF PRIMARY PROCESS VARIABLE Date - Date of last calibration, set by user Upper Range Value - Primary Variable Value in engineering units for 20mA point, set by user Lower Range Value - Primary Variable Value in engineering units for 4mA point, set by user Upper Sensor Limit - Set by manufacturer Lower Sensor Limit - Set by manufacturer Sensor Minimum Span - Set by manufacturer PV Damping - Primary Process Variable Damping Factor, set by user Message - Scratch pad message area (32 characters), set by user Loop Current Transfer Function - Relationship between Primary Variable digital value and 4-20mA current signal Loop Current Alarm Action - Loop current action on device failure (upscale/downscale) Write Protect Status - Device write-protect indicatorHART ADVANTAGES

TRANSDUCER BLOCK:- Generates the actual digital signal representation of the process parameter.ZERO & SPANNING BLOCK:- T he upper and lower range values are used to produce the transducer value from above to correspond to a 4mA signal for the lower range and a 20mA signal for the upper range in the % form. In addition an appropriate transfer function (e.g., linear, square root, quadratic, cubic spline, etc.) may be applied .DAQ BLOCK:- Produces the 4-20ma signal, insuring that 0% equals exactly 4 ma and 100% equals 20ma.

WIRELESS HARTWireless HART Networks consists of Wireless HART field devices, at least one Wireless HART gateway, and a Wireless HART network manager. These components are connected into a wireless mesh network supporting bi-directional communication from HART host to field device and back.

Network Manager

The Network Manager is an application that manages the mesh network and Network Devices. The Network Manager performs the following functions: - Forms the mesh network - Allows new devices to connect to the network - Sets the communication schedule of the devices - Establishes the redundant data paths for all communications - Monitors the network GatewayThe Gateway Device connects the mesh network with a plant automation network, allowing data to flow between the two. The Gateway Device provides access to the WirelessHART devices by a system or other host application.Field DevicesThe Field Device may be a process connected instrument, a router or Hand Held device. The WirelessHART network connects these devices together. -Router Device:A device to improve network coverage (to extend a network) capable of forwarding messages from other Network Devices. - Process Connected Instrument:Typically a measuring or positioning device used for process monitoring and control. It is also capable of forwarding messages from other Network Devices. - WirelessHART Adapter:A device that allows a HART instrument without wireless capability to be connected to a WirelessHART network.